It is well known in naval architecture that the tonnage of hydrofoil type craft is limited currently to about 400 tons, because the weight increase of a hydrofoil craft is much faster than the lifting force from foils when the dimensions of the vessel are increased. The tonnage increases cubically by its dimensions while the lifting force from the foils increases squarely by its dimensions.
It is also well known that the power transmission system on retractable foil type hydrofoil craft is very complicated and often causes maintenance and operational problems resulting from many delicate moving elements enclosed in the movable spidery struts.
It is also well known in naval architecture that it is very inconvenient for a fixed foil type of hydrofoil craft to rest at a limited depth of harbor because the extension of foil planes may hit the bed of the harbor: especially for a large tonnage vessel with long and deep fixed foils.
It is also well known that the speed of a displacement type surface ship is greatly limited by wave formation and resistance resulting from these waves. As the speed of a ship increases its Froude number increases, this number being a relationship dependent upon ship's speed. At Froude numbers of 0.5 and greater, wave resistance increases at a very fast rate. This phenomenon limits the speed of displacement type surface ships to a maximum Froude number of about 1.3.
It is further well known in naval architeture that a submarine operating at a depth below the surface of 3 times the diameter of the hull or greater, experiences a negligibly small wave resistance; nearly all of its resistance being frictional and eddy making resistance. Operation at depths of more than 3 diameters eliminates a crucially important limitation to the speed experienced by all the conventional surface ships, since the wave making resistance of a submarine increases with speed at a much lower rate. Therefore, the top speed of a submerged submarine is potentially much higher than that of the displacement surface ship of the same length and immersed volume.
The objective of this invention is to provide a high speed vessel system having large tonnage as a submarine with the advantage of cruising stability, operational flexibility, simplicity and comfortability as a retractable foil type hydrofoil craft.